JPS63139090A - Method for growing single crystal - Google Patents

Abstract

PURPOSE:To obtain the title high-quality single crystal by detecting the variations in the weight of the growing crystal at any time to calculate the crystal diameter, and correcting the crystal diameter in accordance with the program preset under the specified conditions during growth to control the form of the shoulder part with good reproducibility. CONSTITUTION:For example, the Nd:YAG single crystal material 2 (the material obtained by doping high-purity Al2O3 and Y2O3 with 0.8at% Nd, weighing the appropriate amts. of both materials, and mixing the materials) is charged in the Ir crucible 1 of the single crystal growth device, an electric power is impressed under the command of a personal computer 5 on a high-frequency coil 3 through a D/A conversion circuit 7, an analog controller 8, and a high-frequency oscillator 9 to melt the material, and then pulling up is started. The variations in the weight and high-frequency power are detected at any time with use of a signal 4 from a load cell or a signal 10 from a vacuum thermocouple 10 to calculate the crystal diameter Di. When the Di does not conform to the equation (alpha is 0-15% of Dx and beta is 0-10% of Dx), Dx is set at Dx=Di, the output of the high-frequency power is controlled while correcting the Dx of the preset program, and the shoulder part is formed to grow a single crystal.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is a high quality YAG (Y2Al5O12)! This invention relates to shape control from the start of pulling to shoulder extension in the growth of L crystal or Nd:YAG (YAG l: Nd2O3 doped) single crystal.

(Prior Art) Nd:YAG single crystals are usually produced by a pulling method (Czochralski method). The technical issues when producing a single crystal by the pulling method are firstly to produce a high-quality crystal that meets the purpose, and secondly to produce a long crystal with a predetermined diameter. First.

Challenges include the use of high-purity raw materials, stabilization of the atmosphere and temperature during growth, and pressure control. Regarding the second problem, several automatic growth methods using gravimetric methods or optical methods have been proposed. It is a method of pulling up a mechanical line while irradiating it with a laser beam (Japanese Patent Laid-Open No. 59-549
4) A method of having a reference voltage generation mechanism corresponding to the differential value of the amount of weight reduction (Japanese Patent Publication No. 54-4345), and a method of keeping the temperature of the load cell constant to improve the accuracy of the weight signal (Japanese Patent Publication No. 54-4771). be.

These all show the configuration of an automatic growing system, and do not show any specific control method for controlling the diameter, especially the shape control method for the part that enters the straight trunk (shoulder part) after the start of pulling. Furthermore, there are no practical examples of automatic diameter control for growing high-quality Nd:YAG single crystals, and of course, no examples have been published. In other words, since the Nd:YAG single crystal is pulled at a very high temperature and at a slow pulling speed (0°5 to 1 mm/ur), and because it is used in the length direction of the crystal, it is necessary to develop a highly reliable system that is stable over a long period of time. Therefore, the reality is that automatic training is considered difficult. Therefore, the growth of Nd:YAG single crystals is carried out by skilled and experienced persons.

(Problem to be solved by the invention) The growth temperature of the Nd:YAG single crystal is higher than that of other oxide single crystals (
For example, GGG, etc.), it is extremely high compared to GGG, etc.), so even the slightest change in the material or composition of the heat-insulating refractory will affect the temperature history. For this reason, the seeding temperature is different every time, and the shoulder shape control method is also different. In particular, Nd:YAG single crystals are very sensitive to thermal changes. For this reason, in order to maintain stability, the refractory structure has become more complex, and the monitoring window for crystals has become extremely small, making it difficult to observe the growth state. Under these circumstances, when growing crystals, workers used their many years of experience to create shoulders or control diameters based on changes in weight, etc. Therefore, even an experienced person may fail to control the shape of the shoulders, and of course, an inexperienced person may fail to control the shape of the shoulders.
Growing G single crystals is difficult. In particular, it was impossible to grow single crystals of high quality.

The purpose of the present invention is to solve this problem and provide a method that allows anyone to control the shape of shoulder construction with good reproducibility.

(Means for Solving the Problems) The present invention enables detection of weight changes and high frequency power during single crystal growth, determines shape control conditions for shoulder formation during growth,
In addition, in a controllable single crystal growth method using the Czochralski method, the crystal diameter (Di) is calculated while constantly detecting changes in the weight of the grown crystal, and this Di and the target diameter (Dx) are determined so that Dx-a≦Di< Dx + β (however, α is 0 to 1
5%, p is 0 to 10%), Dx = D
Dx of the predetermined program after setting to i
A single crystal growth method characterized by growing while modifying.

(Function) The present invention utilizes the above-described structure and method to produce high-quality Nd:YAG.
We have found a method to control the ideal shoulder shape of single crystals.

In order to control the shape of ideal shoulder construction, the present inventors
We analyzed in detail the relationship between the change in the diameter of the grown single crystal and high-frequency power, and conducted various studies. As a result, from the changes in the crystal and the changes in high-frequency power, it is ideal to grow high-quality Nd:YAG single crystals by controlling the shape while changing the target diameter in parallel with controlling the high-frequency power under certain conditions. It became clear that it could be done. Target diameter (Dx
) is the relationship between the high frequency power and the diameter of the grown crystal (Di).
When Di is smaller than Dx, the high frequency power must be kept constant or decreased, and conversely, when Di is larger than Dx, the high frequency power must be increased. The magnitude of this high frequency power is D
Although it is determined by the difference between x and Di, when the amount of change in high frequency power is increased, the quality of the Nd:YAG single crystal deteriorates significantly. It has become clear that in even more extreme cases, it will break. Therefore, in order to control the crystal diameter while maintaining high quality, it has become necessary to vary the amount of high frequency power within ±0.05% or within 2% fat under certain conditions. Therefore, the range in which the shape can be controlled under certain conditions of high-frequency power was analyzed in detail with respect to the difference between Di and Dx, that is, α and i3.

As a result, α is 0 to Dx as shown in Figure 1(a).
It has been found that shape control with guaranteed quality can be achieved if p is within 0 to 10%. By this D
It has also become clear that when i is other than Dx-α≦Di≦Dx+p, the change in high-frequency power for approaching Dx becomes larger than a certain condition, and the quality deteriorates significantly. Furthermore, α
It has also become clear that the values of , β change depending on the history (deterioration of refractories, changes in the thermal environment, etc.) after the start of pulling. Therefore, we investigated a control method to ensure quality even when Di is other than Dx-α≦Di≦Dx+β. As a result, when Di is other than Dx-α≦Di≦Dx+β, Dx should be set to Dx = Di. (Figure 1b) If you create a new program for Dx to be the target in the future and perform shape control according to this program, high frequency Changes in power could be made under certain conditions. As a result, high quality crystals were obtained.

As mentioned above, by using the single crystal growing method of the present invention, especially the shape control method for shoulder making, anyone can ideally make the shoulder, and high quality crystals can be grown, so that it can be used industrially. Great value.

Next, the present invention will be explained with reference to examples.

(Example) 85φX 100h X 1 of the single crystal growth apparatus shown in Figure 2
．． Add 2100 g of Nd:YAG single crystal raw material (high purity Al2O3, Y2O3+: doped with 0°8 at% Nd, weighed and mixed appropriate amounts of each) to a 7 ton Ir crucible 1, installed a heat-retaining refractory, and placed the center of the high frequency coil 3. It was established in

In response to a command from the personal computer 5, the analog controller 8 and the high frequency oscillator 9 are connected via the D/A converter circuit 7.
Electric power was applied to the high frequency coil 3 to melt the raw material 1 in the Ir crucible. Next, a YAG single crystal (not doped with Nd) was used as a seed crystal <111>, immersed in the solution, and after confirming that the temperature conditions were optimal, pulling was started.

The pulling speed was 1 mm/nr and the rotation speed was 2 Orpm. Set the target diameter (Dx) program so that the grown crystal thickens by approximately 30 degrees after starting pulling, and use the signal 4 from the load cell or the signal from the vacuum thermocouple 10 to generate a high frequency signal using a personal computer. Controls power output. Dx 10 hours after starting pulling
is 12.5φ, while the crystal diameter (Di) is β. It became 8φ. For this reason, the output change rate of high frequency power is β11v/h
r to 15 pv/hr and Dx to β. 8φ
The Dx program after that was corrected. Furthermore, after 28 hours, Dx became 28φ and Di became 25φ, so the output change rate of high frequency power was changed from 18 pv/hr to 12 pv/hr.
At the same time as changing to hr, Dx was changed to 25Φ and the subsequent Dx program was modified.

After 33 hours, Di reached 30φ, so I opened my shoulder and controlled the diameter with personal computer 5 while measuring about 16mm.
After 0 hours, the crystal was separated and the growth was completed. The grown crystal is a very smooth counterfeit without any corners, and furthermore,
When the birefringence of a rod (4Φ×10 mm) cut out from the crystal was measured by phase difference, 4n=IX10-7 or less was obtained, and a high-quality Nd:YAG single crystal with very little optical distortion was obtained.

(Effects of the Invention) According to the present invention, anyone can build ideal shoulders, and it is effective for automatic growth.

[Brief explanation of the drawing]

Figure 1 (aXb) is a diagram explaining the shape control of shoulder making according to the present invention, Figure 2 is a diagram showing an example of a single crystal growth apparatus, 1 is an Ir crucible, 2 is a Nd:YAG single crystal, 3 is a diagram showing an example of a single crystal growth apparatus. High frequency coil, 4 is a load cell, 5 is a personal computer, 6
is an A/D converter, 7 is a D/A converter, 8 is an analog controller, 9 is a high frequency oscillator, and 1o is a vacuum thermocouple. l Figure 1 Time (1) Time (1)

Claims (1)

[Claims] In the single crystal growth method using the Czochralski method, which detects the weight of the single crystal during growth and controls the crystal by changing the rate of increase according to a predetermined program,
In order to control the crystal diameter during growth to a predetermined crystal diameter (Dx), the crystal diameter (Di) is calculated from the change in crystal weight, and Di
is Dx-α≦Di≦Dx+β (however, α is 0 to 1 of Dx
5%, β is other than 0 to 10% of Dx, Dx = D
After setting i, Dx of the predetermined program
A single crystal growth method characterized by growing while modifying.